The present invention relates to a semiconductor device, and, in particular, to a semiconductor device having a layered interconnect structure.
In recent large-scale-integration, for high-performance semiconductor devices, copper (Cu) interconnects are being employed since they have a lower electrical resistance than conventional aluminum (Al) interconnects. However, diffusion of copper (Cu) atoms into silicon (Si) substrates or insulating films tends to degrade the characteristics of such devices. To prevent such copper (Cu) diffusion, a diffusion barrier is formed adjacent to the copper (Cu) film. As the material for the diffusion barrier, high-melting-point metal films of, for example, titanium nitride (TiN), tungsten (W) or tantalum (Ta) have been investigated, as discussed in the Nikkei Microdevice (for July 1992, pp. 74–77).
Large-scale-integration semiconductor devices with fine patterns receive a high-density current, in which, therefore, atoms are diffused owing to electron streams flowing therein and to the heat that is generated by the flow of electrons, thereby to cause voids and interconnect breakdowns. The problem with the devices is the result of so-called electromigration. As compared with aluminum (Al) films, copper (Cu) films, which have a higher melting point, are difficult to diffuse, and are therefore expected to have good electromigration resistance. However, layered interconnect structures, in which a diffusion barrier of, for example, a titanium nitride (TiN) film, a tungsten (W) film or a tantalum (Ta) film, is kept in contact with a copper (Cu) film, do not have a satisfactory electromigration resistance, and therefore often pose the problem of voids and interconnect breakdowns.